Chatham Callan, Associate Professor of Aquaculture

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Associate Professor Callan researches rearing methods for Hawaiian reef fish, with applications in the aquarium trade and local fishing industries.

Chad Callan casual portrait and an aerial view of research facility ponds and buildings located at rocky coastline.
Associate Professor Chad Callan and an aerial view of UH Hilo’s Pacific Aquaculture and Coastal Resource Center located in Keaukaha, Hilo Bay, where he is conducting teaching, research, and outreach activities. (Photos: College of Agriculture, Forestry, and Natural Resource Management/UH Hilo)

Posted Feb. 23, 2026.

Chatham “Chad” Callan is an associate professor of aquaculture at the University of Hawaiʻi at Hilo. His area of research is in developing rearing methods for Hawaiian reef fish, with applications in the aquarium trade and local fishing industries.

Callan received his master of science in marine biology (2000) and a doctor of philosophy in marine biology (2007) both from the University of Maine. He arrived at UH Hilo as an associate professor of aquaculture in 2023 after teaching at Hawaiʻi Pacific University on Oʻahu for over 15 years. At HPU, he also conducted research and later served as program director at the Oceanic Institute’s Finfish Program where he managed all aspects of the program, from administrative work to trial development and research.

In addition to his position at UH Hilo, he is currently serving as cooperating graduate faculty at UH Mānoa’s marine biology graduate program.

Ornamental aquaculture

Callan researches sustainable rearing methods for coral reef fishes not commercially available in the aquaculture trade. Usually, these fish are taken from the wild, but developing commercially viable methods of raising fish lessens the strain on wild-caught fish populations and the coral reefs they support. Many of these fish have not been studied in an aquaculturing context before, so little is known on how to properly rear them in a lab or commercial context.

“I hope to rectify this through research and improve commercial fish production for the aquarium trade,” he says.

Yellow fish against a black background.
The yellow tang (Zebrasoma flavescens) is one of the most popular marine aquarium fish, this one in the Aquarium-Muséum of Liège, Belgium. Yellow tang naturally occurs in reef environments. (Photo: Luc Viatour/Wikipedia)

Callan says his most significant contribution to the literature is an article outlining a new feeding protocol for yellow tang, research that “has since transformed how marine ornamental aquaculture is being done for other species.”

“My lab was the first to culture this species after nearly 20 years of R and D trying to make it happen,” he says. “This work paved the way for the culture of other, similar, reef species that are of high importance to the aquarium trade. Culture of these fish species helps reduce fishing pressure on coral reefs.”

In another project, Chatham and his research team uncovered a previously unknown stage in the life cycle of the Hawaiian cleaner wrasse.

“In my current research with Hawaiian cleaner wrasse, we learned that this fish goes into a semi hibernation type state during its metamorphosis to juvenile form,” explains Callan. “During this time, they basically make a little mucous cocoon and nearly vanish from the rearing tanks. We had previously assumed they had all perished during this phase, but recently were very surprised to see nearly 60 emerge from this state and fill the tank once again. This marked another first for this species, as after we raised this batch they were made commercially available for the first time as a cultured alternative to wild fish.”

This Hawaiian cleaner wrasse research is ongoing at UH Hilo’s Pacific Aquaculture and Coastal Resource Center located in Keaukaha at the edge of Hilo Bay, where Callan was conducting research for several years before coming on board as UH Hilo faculty in 2023. The research team has been culturing endemic Hawaiian species, such as potters angelfish and Hawaiian cleaner wrasse, among others, since 2015, and recently made the significant headway with the cleaner wrasse.

“We plan to keep working with this species, and hope to continue improving methods for their rearing so that commercial offerings will become more frequent,” says Callan in a social media post. The work includes caring for broodstock, producing live feeds, and caring for the delicate larvae; “this work is a labor of dedication,” he says.

He’s also currently working on developing culture methods for other coral reef fish species that have not been commercially produced yet.

Marine stock restoration

Callan is also working with state agencies to restore nearshore fisheries. Previous stock restorations programs for moi and mullet in the late 1990s to early 2000s showed promising results building up local fisheries but were ended due to a lack of funding.

“A major goal within the next decade is partnering with the state to get the moi and mullet programs back up and running again,” says Callan. “Our work aims to help reduce impacts on coral reef environments and help restore nearshore fisheries with species that have been experiencing declines over the past several decades.”

Another research goal is working together with community leaders managing loko iʻa (traditional fishponds) to restock the ponds and find ways to produce fish depending on the condition of the fishpond. Fish such as mullet, moi, āholehole, and milkfish are all species of interest for Callan and the fishpond managers across the state who wish to restore these culturally significant areas to the point where the fish can once again be grown and harvested.

“I’d really love to see a successful stock restoration program for moi and mullet be re-started again,” he says.

A diagram of fish development, an aerial of the entire island, an aerial of the fishpond studied, and aerial of the fishpond.
Fig. 1 from the loko iʻa and climate change study: A map of the study area and model schematic. (A) map of Oʻahu, (B) Kāneʻohe Bay, (C) Heʻeia fishpond, and (D) a conceptual diagram of the model framework and different scenarios tested, including warming (outlined in red), nutrients (outlined in green) and fish restocking (outlined in blue). The boundaries highlighted in panel B are approximate and for illustrative purposes only to demonstrate the different habitats in the model. (Creative Commons License, click/tap for full size)

In relation to this work, Callan and a research team have investigated loko iʻa and the impacts of climate change. This study assesses how climate change may affect loko iʻa productivity, as well as how nutrient flow restoration and restocking may mitigate some of these effects.

“We found that although rising water temperature may lead to declines in fish density, loko iʻa fish populations were more resilient to rising water temperatures than those in the surrounding estuary,” write the collaborative authors of the study. “Notably, the combined benefits of fisheries effort regulations, nutrient flow restoration, and restocking were found to offset some of the potentially negative effects of warming on fish populations and substantially increase short- and long-term estuarine and loko iʻa fish density. However, long-term population trends were still primarily dictated by emissions scenarios and their associated temperature projections. In the face of rising water temperatures, biocultural restoration may be especially important for enhancing fish populations and increasing social-ecological resilience.”

Teaching and workforce development

Along with two aquaculture classes Callan currently teaches as a primary instructor, students work directly with him at UH Hilo’s aquaculture center, where much of his research takes place.

Aerial view of the aquaculture center located at the edge of Hilo Bay.
Aerial view of UH Hiloʻs Pacific Aquaculture and Coastal Resource Center located in Keaukaha, Hilo Bay. (Photo: PACRC/UH Hilo)

“Students work with us directly here at the Pacific Aquaculture and Coastal Resource Center, assisting with fish care, feeding, recording data, cleaning tanks, etcetera,” he says. “They get great hands-on experience that makes them much more marketable post graduation. I also help mentor undergraduate students on their capstone projects as well as supervise graduate students.”

Undergraduates are encouraged to do independent research projects for thesis or capstone work and use the aquaculture facility to develop various research and fish rearing skills. The center also employs students to help around the facility caring and feeding fish, cleaning tanks, and recording data, all invaluable hands-on experience for those hoping to get into the field.

Callan says there are an increasing number of aquaculture-related positions around the islands as the industry continues to grow and diversify.

“As the fastest growing food production sector in the world, aquaculture stands on the forefront of future food production, especially here in Hawaiʻi,” he says.

Alongside graduate students and doctoral candidates doing research at the aquaculture center, the facilities also host elementary and high school student groups. This gives Callan the chance to teach visiting students about the work being done at the center, an essential part of the scientific outreach portion of his research.

By Samantha Dane, a biology major at UH Hilo and student science writer for the Office of the Chancellor.